(Nuclear RNase P )

In molecular biology, nuclear ribonuclease P (RNase P) is a ubiquitous endoribonuclease, found in archaea, bacteria and eukarya as well as chloroplasts and mitochondria. Its best characterised enzyme activity is the generation of mature 5'-ends of tRNAs by cleaving the 5'-leader elements of precursor-tRNAs. Cellular RNase Ps are ribonucleoproteins. The RNA from bacterial RNase Ps retains its catalytic activity in the absence of the protein subunit, i.e. it is a ribozyme. Isolated eukaryotic and archaeal RNase P RNA has not been shown to retain its catalytic function, but is still essential for the catalytic activity of the holoenzyme. Although the archaeal and eukaryotic holoenzyme s have a much greater protein content than the bacterial ones, the RNA cores from all three lineages are homologous -- the helices corresponding to P1, P2, P3, P4, and P10/11 are common to all cellular RNase P RNAs. Yet there is considerable sequence variation, particularly among the eukaryotic RNAs.